The main application of the invention is for use in burners for a rotary tubular furnace in which at least 80% of primary combustion air is delivered via at least two concentric ducts disposed around any fuel feed duct and via a third, central feed duct into which the remaining not more than 20% of the primary air is injected.
In a preferred embodiment, of said two concentric annular ducts feeding said burners with at least 80% of their primary air, one of them feeds the air in the form of a swirling current of air having peripheral flow components, and the other feeds air in the form of an axial flow having flow components that are substantially axial; said two primary air flow ducts are thus disposed radially outside any fuel duct, and in particular at least one annular duct for feeding pulverized coal; the central duct inside which at least one fuel feed pipe is slid, at least for starting purposes, is partially obstructed by a flame stabilizer in the form of a flange surrounding the central opening into which said pipe opens out, and has openings for passing a portion of the primary combustion air, i.e. said not more than 20%, and even in fact not more than 10% of the primary air, in such a manner that in the central zone situated downstream from said stabilizer no significant combustion of the fuel takes place, such that said central zone can be said to be "dead"; such a burner is described and claimed in European patent 421 903 published on Apr. 10, 1991 and filed by the same Applicant as for the present invention.
The present invention can be considered as being an improvement applied to such burners and more generally to any burner that can be considered as being a "modern" burner, having fuel and combustion air feed ducts in the above-defined main application, which ducts form a nozzle assembly for mounting on an-orifice provided for that purpose in the wall of an enclosure forming the hearth of the furnace or combustion chamber, and around which secondary air is delivered.